The present invention relates to a valve gear for an internal combustion engine, the engine comprising one or more cylinders and a piston reciprocating therein, as well as a cylinder head mounted on an upper end of the cylinder. At least one exhaust valve opening into an exhaust channel and at least one suction valve opening into a suction channel are arranged for each cylinder, these valves being operated by transmission of a cam shaft or the like.
In conventional internal combustion engines (four-stroke engines), the suction and escape valves of each cylinder are simultaneously open for a predetermined period of time due to engine flushing (exhaust gases). For example, the suction valve will open by 20 crank degrees before the end of the exhaust stroke, i.e. the top dead center, while the escape valve will close by 15 crank degrees after the dead end center. In such a case, the suction and escape valves are thus simultaneously open by 35 crank degrees. As a result, incombustible fuel-air mixture will enter the exhaust channel, whereby, due to the heat and incombustability of the exhaust gases (there is insufficient oxygen in the exhaust channel needed for combustion), the exhaust gases will contain a large quantity of detrimental carbon monoxide and hydrocarbons due to the incomplete combustion.
Due to the simultaneous opening state of the suction and escape valves, it has not been possible to increase the supercharger pressures in conventional engines provided with turbo-supercharges as desired, since excess-pressure air produced by the superchargers will flow directly out of the escape valves. For this reason, inter alia, a certain considerable delay is always present in conventional engines provided with superchargers when pressing the gas pedal, while the engine does not react immediately to the pressing of the gas pedal.
Additionally, since air can flow in such structures into the escape channel, this will bring along an incomplete combustion in the escape channel, as a result of which the exhaust gases will contain a large quantity of detrimental carbon monoxide. If the valves do not have a common opening-state time, a large quantity of remainder exhaust gases will, in the cases concerned, remain in the combustion space of the engine. In such a case, the suction air entering the engine will heat and its volume will increase. Thus, filling the cylinder with the fuel-air mixture will remain insufficient, and formation of the carbon monoxide will similarly occur to a great extent.
For reducing detrimental exhaust gases, an attempt has been made to develop internal combustion engines, for example, in such a way that combustion therein would be as complete as possible. One solution to achieve this goal has previously been, for example, varying the compression ratio of the engine and especially the volume of the combustion space during the engine operation. Such solutions have been previously described, for example, in EP application No. 82,925; DE application No. 3,526,961; and GB application No. 2,000,551. In U.S. Pat. Nos. 2,988,071 and 2,979,046, solutions have in turn been described in which the opening-state times of the suction and escape valves have been limited so that there simultaneous opening-state time would be as short as possible. In both these latter U.S. Patents, this has been achieved so that the suction and escape valves are arranged "one within the other" coaxially, with their timing having been achieved in the previously-described manner.
In the previously-noted publications, in which the EP, DE and GB publications relate to engines provided with a varying compression ratio, the construction has generally required a fairly complex counter-piston arrangement or the like. Solutions in accordance with the prior art also include several other drawbacks. In the previous-described EP publication, it can be emphasized that in an engine according to this reference, there is always a space between the counter-piston and the actual piston, in which space remainder gases may remain. In this solution, gas exchange may thus not be sufficiently satisfactory, whereby most of the advantages, which the solution of the EP publication concerned is intended to achieve, will be lost. The changing of the compression ratio into a forced-operation state during engine operation at every crankshaft revolution requires, in the solution according to the EP publication, also a very complex crank and lever mechanism.